Version control

Hi
If two people are syncing to the same google docs folder. Is it possible for both to open the same document to work on and both save a new version at the same time? I don't, of course, want to do that. I want either, the second user to open the document to be prevented from opening it until the first user has finished their edits, or I want us to be notified that we've clashed and we need to do something about it. The worst scenario would be that neither of us are aware that we've worked on the same document at the same time and one of us loses our work!
Thanks